The present invention relates to an apparatus and a method of observing surface configurations by using an electron beam, and especially provides an apparatus and a method by which observation of either configurations of the bottom of a deep hole or residues therein, used frequently in semiconductor processes, can be permitted.
The scanning electron microscope, in which an electron beam is scanned on a specimen and secondary electrons generated from the specimen are detected, has been utilized widely in the fields of biology and engineering. Especially, in the semiconductor industry, high-integration formation has been advanced and as a result, inspection based on optical microscopes has become impossible, and the utilization of the scanning electron microscope has been promoted. In a scanning electron microscope used for semiconductors, it is conventional to use an electron beam of low energy of 1 keV or less in order to avoid charging on insulators.
In the semiconductor industry, the scanning electron microscope is utilized for not only inspection of appearance of completed semiconductors but also inspection in mid-course of the manufacturing process. For example, it is used for inspection of appearance, inspection of dimension and inspection of through-holes in mid-course of the process.
As a result of the advancement of high-integration formation of semiconductor devices, it has become impossible for the method using the conventional scanning electron microscope to inspect openings of through-holes.
Referring to FIG. 2, problems encountered in observing a deep hole with the conventional scanning electron microscope will be described. FIG. 2 shows a case where a primary electron beam 1 of low energy irradiates a flat portion and a hole 3 of a specimen Thanks to the absence of any obstacles, almost all of the number of secondary electrons 2 generated at the flat portion can be detected. Similarly, reflection electrons concurrently discharged can also be detected In the case of irradiation of the hole 3, however, generated secondary electrons 2 impinge on the side wall of the hole 3 and consequently cannot escape from the hole 3 to the outside. The energy of reflection electrons is higher than that of secondary electrons but is not so high that the reflection electrons can penetrate through the side wall, and the reflection electrons are thus blocked by the side wall.